Remodeling Protein Interfaces to Regulate Recognition

Abstract

The protein proopiomelanocortin (POMC) is a precursor several nerve peptide hormones, including MSHs, ACTH, CLIP, LPH, b-endorphin, and the Joining peptide (JP). The biological activity of POMC derived peptides have been well studied except for JP. To investigate the biological function of JP, we chemically synthesized JP by an Fmoc solid phase method. However, the yield of the synthesized JP was poor and a highly efficient a/b-rearrangement in the Asp-Gly sequence was observed. Therefore, we evaluated the rearrangement of the Asp-Gly sequence under several conditions to estimate the biological activity and the stability of the correct configuration of JP. For this purpose, JP was chemically synthesized by ordinary Fmoc and Boc solid phase methods. After deprotection, JP was separated and identified by reverse-phase HPLC and MALDI-TOF/MS, respectively. The rearrangement of the Asp-Gly moiety was observed in the case of the Fmoc method but was not significant in the case of the Boc method. To estimate the stability of the Asp-Gly moiety, JP was treated with several buffers in the pH range of 1-8. The a/b-rearrangement was gradually increased in a pH-dependent manner and was significantly observed under strongly acidic conditions. In addition, salt effects for the rearrangements were also estimated. The results will be discussed in this paper.